Recently, the air pollution problems are becoming increasingly serious in our country and its neighboring regions. In particular, the concentration of fine suspended particles (e.g., Particulate Matter 2.5, PM2.5 and Particulate Matter 10, PM10) is often too high. Hence, the monitoring of the concentration of suspended particles in the air is getting attention. However, since the air flows with the change of the wind direction and the air volume and the current air quality monitoring stations for detecting suspended particles are mostly fixed points, it is impossible to confirm the concentration of suspended particles in the current surroundings. Hence, a miniature portable gas detecting device is needed. It allows users to detect the concentration of suspended particles around the surrounding anytime and anywhere.
Moreover, the current gas detecting device is often only capable of detecting a single gas. In addition to the suspended particles, there are many gases harmful to the human body in daily life. If the harmful gases cannot be detected immediately, the health of the human body is adversely affected.
Moreover, the user's demands for detecting different gases may be varied according to different places (e.g., factories, offices or homes). For example, the gas sensors for detecting the volatile gases or the toxic gases (e.g., the gases that cause the inhalation injuries) are suitably used in factories. The carbon monoxide sensors, the carbon dioxide sensors, the temperature sensors or the humidity sensors are suitably used in homes or offices. Since the commercially available gas detecting device is an integral gas detecting device, some drawbacks occur. For example, the type of the gas to be detected has been determined before the gas detecting device leaves the factory. The type of the gas to be detected cannot be changed by the user according to the user's requirement. Consequently, the gas detecting device detects the gas out of the user's requirement or fails to detect the gas according to the user's requirement. In other words, the conventional gas detecting device is not user-friendly. Moreover, it is difficult for the user to select the suitable gas detecting device. For solving the above drawbacks, it is important to provide a gas detecting device for detecting the gas according to the user's requirement.